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Date: Thu, 15 Oct 2009 09:00:18 +0530 From: Bharata B Rao <bharata@...ux.vnet.ibm.com> To: Peter Zijlstra <a.p.zijlstra@...llo.nl>, linux-kernel@...r.kernel.org, Dhaval Giani <dhaval@...ux.vnet.ibm.com>, Balbir Singh <balbir@...ux.vnet.ibm.com>, Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>, Gautham R Shenoy <ego@...ibm.com>, Srivatsa Vaddagiri <vatsa@...ibm.com>, Ingo Molnar <mingo@...e.hu>, Pavel Emelyanov <xemul@...nvz.org>, Avi Kivity <avi@...hat.com>, Chris Friesen <cfriesen@...tel.com>, Paul Menage <menage@...gle.com>, Mike Waychison <mikew@...gle.com> Subject: Re: [RFC v2 PATCH 4/8] sched: Enforce hard limits by throttling On Wed, Oct 14, 2009 at 03:18:54PM +0200, Herbert Poetzl wrote: > On Wed, Oct 14, 2009 at 05:20:03PM +0530, Bharata B Rao wrote: > > On Wed, Oct 14, 2009 at 11:17:44AM +0200, Peter Zijlstra wrote: > > > On Wed, 2009-10-14 at 09:11 +0530, Bharata B Rao wrote: > > > > On Tue, Oct 13, 2009 at 04:27:00PM +0200, Peter Zijlstra wrote: > > > > > On Wed, 2009-09-30 at 18:22 +0530, Bharata B Rao wrote: > > > > > > > > > > > diff --git a/include/linux/sched.h b/include/linux/sched.h > > > > > > index 0f1ea4a..77ace43 100644 > > > > > > --- a/include/linux/sched.h > > > > > > +++ b/include/linux/sched.h > > > > > > @@ -1024,7 +1024,7 @@ struct sched_domain; > > > > > > struct sched_class { > > > > > > const struct sched_class *next; > > > > > > > > > > > > - void (*enqueue_task) (struct rq *rq, struct task_struct *p, int wakeup); > > > > > > + int (*enqueue_task) (struct rq *rq, struct task_struct *p, int wakeup); > > > > > > void (*dequeue_task) (struct rq *rq, struct task_struct *p, int sleep); > > > > > > void (*yield_task) (struct rq *rq); > > > > > > > > > > > > > > > > I really hate this, it uglfies all the enqueue code in a horrid way > > > > > (which is most of this patch). > > > > > > > > > > Why can't we simply enqueue the task on a throttled group just like rt? > > > > > > > > We do enqueue a task to its group even if the group is throttled. However such > > > > throttled groups are not enqueued further. In such scenarios, even though the > > > > task enqueue to its parent group succeeded, it really didn't add any task to > > > > the cpu runqueue (rq). So we need to identify this condition and don't > > > > increment rq->running. That is why this return value is needed. > > > > > > I would still consider those tasks running, the fact that they don't get > > > to run is a different matter. > > > Ok, that's how rt also considers them I realize. I thought that we > > should update rq->running when tasks go off the runqueue due to > > throttling. When a task is throttled, it is no doubt present on its > > group's cfs_rq, but it doesn't contribute to the CPU load as the > > throttled group entity isn't there on any cfs_rq. rq->running is used > > to obtain a few load balancing metrics and they might go wrong if > > rq->running isn't uptodate. > > for all practical purposes throttled tasks _are_ running > (i.e. they would like to run, but the hardware/software > doesn't allow them to do more work) ... Ok, I will take a re-look at this and see if I too can consider them as running and don't touch rq->running which should simply some code. > > > Do you still think we shouldn't update rq->running ? If so, I can get rid > > of this return value change. > > Linux-VServer marked throttled tasks as 'H' (on hold) > but counted them as running, which seems to work fine > and reflect the expected behaviour ... So a new task state 'H' ? Thanks for your comments. Regards, Bharata. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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